The present invention concerns the field of spinning technology and concerns a method of piecing after interruption of the spinning process. The inventive method serves for piecing up a yarn or thread formed on a spinning machine, or on a spinning position of a spinning machine respectively, from a staple fibre material, e.g. after a can change, a bobbin change, a thread breakage, or after another disturbance of the spinning process. The method also can be used for starting or restarting the spinning process. The present invention furthermore concerns a spinning position equipped for implementing the inventive method.
Spinning machines for spinning staple fibre material usually comprise a large number of spinning positions, a yarn or thread being spun on each spinning position from a longitudinally extending fibre array. In this arrangement the longitudinal fibre array first is rendered finer, or refined respectively, i.e. the quantity of fibres per unit length is reduced by a draft being applied. The fibre array rendered finer then is spun into a yarn or thread, twist being applied, which yarn or thread then is taken up on a bobbin. For refining, the fibre array is, for example, subject to a draft applied using a drafting system or is opened using an opening roll. For imparting twist, various methods are known: e.g. ring spinning, pot spinning, bell spinning, friction spinning, rotor open end spinning, air spinning, etc.
If an interruption of the spinning process occurs, causing an interruption of the cohesion between the yarn spun and the fibre array rendered finer, this cohesion or connection must be re-established; not only for ensuring that the yarn is coherent, but also that the spinning process can be resumed. For re-establishing such connection between the yarn and the fibre array, the free yarn end generated by the interruption, particularly in air spinning methods, is taken upstream against the regular yarn transport direction beyond the twist imparting zone and is positioned. Then, the yarn take-off and the twist imparting devices are started again, and the free end of the refined fibre array is supplied to the twist imparting device in such a manner that during a short transition period the end portion of the yarn and the starting position of the fibre array move through the twist imparting device together. In this process, owing to the twist imparting process, the fibres of the fibre array are whirled, and the starting portion of the fibre array is connected to the end portion of the yarn in a kind of splicing process in such a manner that the spinning process again can be operated in normal manner.
In the spinning start-up process, or the re-starting process respectively, the process can be effected in the same manner, in which arrangement instead of the end portion of the yarn produced before the interruption of the spinning process, an auxiliary yarn is used.
The connection point (also called piecing-zone) in the yarn generated by the piecing-up or the start-up processes, must meet the following requirements:
In order to ensure disturbance-free continuation of the spinning process, the piecing-zone point and its surrounding zone is to present sufficient tensile strength, i.e. normally that this tensile strength is to be at least as high as the tensile strength of the yarn produced during the spinning process.
In order to ensure that the piecing-zone points do not impair yarn quality, the fibre mass per unit length at the piecing-zone point and in its surrounding zone differs from the fibre mass per unit length of the yarn produced in the spinning process only within predetermined, and usually narrow, limits.
In other words this signifies that in case of interruptions of the spinning process the piecing-zones to be generated are to differ as little as possible from the other zones of the yarn produced with respect to strength and fibre mass per unit length. They are to be as invisible as possible, or expressed in other words, be undetectable, and they are to impair further processing and use of the yarn as little as possible, right from the continuation of the spinning process.
Various methods are known using which the abovementioned objectives are aimed at. These methods act onto the free yarn end, onto the free front end of the refined fibre array and/or onto the timing coordination of the movements of the yarn end zone and of the fibre array front end in the twist imparting zone.
It is known e.g. from the publication DE-4240653-A1 that the yarn end zone be roughed up, or that fibre ends be loosened from the dense fibre arrangement of the yarn, and to angle them off the yarn in such a manner that the whirling action together with the newly supplied fibres is improved, and that thus the tensile strength of the piecing-zone is increased.
From the same publication, it also is known that the yarn end zone be prepared for the splicing action in such a manner that the fibre mass gradually decreases towards the yarn end, i.e. that the yarn tapers off towards its end. A yarn end zone tapered off in such manner for splicing then is inserted into a correspondingly tapered front end zone of a longitudinal fibre array (of gradually increasing fibre mass) and the two zones are guided overlapping through the twist imparting zone.
Application of a xe2x80x9cpointedxe2x80x9d front end zone of a fibre array in the piecing-zone process is described e.g. in the publication U.S. Pat. No. 5,802,831 (Murata). According to this publication, a longitudinal fibre array is drafted in a drafting system before twist is imparted, in which arrangement the drafting system on its input side is provided with a pre-drafting zone and on its output side is provided with a main drafting zone. If the spinning process is interrupted, the supply of the longitudinal fibre array to the drafting system is stopped. As the main draft is not stopped, the longitudinal fibre array is severed between the pre-drafting zone and the main drafting zone and there forms a free front end zone. After the interruption, the supply and the draft are correspondingly synchronized with the twist imparting process and the yarn take-up, and are coupled to the corresponding drives. The front end zone of the longitudinal fibre array, which is assumed to be of tapered shape owing to the severing process, in this arrangement first is subject to the main draft, and it is assumed that said tapered zone is drafted correspondingly and thus is supposed to yield an improved piecing-zone.
The method according to U.S. Pat. No. 5,802,831 is further refined according to the publications U.S. Pat. No. 5,809,764 and U.S. Pat. No. 5,934,058 (both Murata) in that the tapered front end zone of the longitudinal fibre array before drafting is shortened by tearing off of a short length, and in that in an air stream applied between the drafting system and the twist imparting zone, the fibre mass of this front end zone is reduced further in a controlled manner.
It proves difficult, using the methods cited, to produce piecing-zones that meet the highest requirements. The yarns pieced according to the methods cited tend to present a weak spot in which the fibre mass is too small immediately after a piecing-zone, or the fibre mass is too large in the zone of the piecing-zone.
Therefore the piecing zone is provided with a fibre mass of up to 200 percent higher than the regular yarn ensuring a tensile strength certainly sufficient for the spinning start-up process, and these piecing-zones, which can be up to 200 mm long, later are detected by a yarn cleaner device and are replaced by correctly produced splicings. This procedure clearly is costintensive.
It thus is an objective of the present invention to create a method for piecing up or starting the spinning process, using which method piecing-zones can be produced meeting higher requirements concerning strength as well as concerning fibre mass than it was achieved with piecing-zones produced using known methods. Furthermore it is an objective of the present invention to create a spinning position equipped for implementing the inventive method. Additional objects and advantages will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
The inventive method is based on the finding that usually in the case of an interruption of the spinning process, the front end zone of a several longitudinal fibre array does not present a noticeable taper and/or that a front end zone of this type also after a drafting process is not suitable for generating a satisfactory splicing. According to the inventive method, thus a front end zone generated by severing, and thus possibly tapered zone, is not subject to a normal draft, but with the help of a corresponding control of the draft in the refining step, a front end zone is formed with an increasing fibre mass as desired. For this purpose, as the spinning process is resumed, during a start-up phase advantageously the supply of the longitudinal fibre array into the refinement zone is controlled in such a manner that it is coordinated to the delivery of the refined fibre array from the refining zone, i.e. that the draft gradually diminishes and that the fibre array delivered presents a fibre mass gradually increasing along its length. Thus essentially a supply control ensures that the draft during the refinement step gradually diminishes (increasing supply speed) until it reaches its value suited for a normal spinning process.
The delivery speed of the refined fibre array leaving the refining zone (or delivery speed of the material into the yarn formation process) can be maintained constant of the time span of diminishing draft (as during the normal spinning process), or it can, in adaptation to a corresponding increase in yarn formation speed, be gradually increased, for facilitating problem-free start-up of the spinning process.
The time span over which the draft of the longitudinal fibre array supplied into the refining process is reduced to a normal value, and the speed profile of this draft reduction, are to be adapted to the length and the form of the tapering yarn end zone. The movement of the yarn end zone through the twist imparting zone is to be adapted in time sequence to the movement of the front end zone of the fibre array delivered from the refinement zone in such a manner that the tapered zones overlap as completely as possible as they move through the twist imparting zone and complement each other mutually to a combined fibre mass, which deviates as little as possible from the fibre mass of the yarn produced during the normal spinning process.
A spinning position equipped for implementing the inventive method is provided, just as known spinning positions, with refining means, twist imparting means and means for taking off the yarn spun. In this arrangement, parts of the refining means arranged on the input side are controlled independently from the parts of the refining means arranged on the output side for a spinning start-up routine, which start-up routine essentially consists in reducing the draft, to which the longitudinal fibre array is subject in the refining means, from a higher value to a normal value. The parts of the refining means arranged on the delivery side and the yarn take-off means can be operated at normal speed during the spinning start-up routine, or can also undergo a spinning start-up routine with gradually increasing speeds.
The spinning position equipped for implementing the inventive method thus is provided with a controllable drive within the spinning position for the parts of the refining means arranged on the input side, or a correspondingly controllable gear train between these parts of the refining means arranged on the input side and a central drive mechanism. The other parts of the spinning position can be driven via simple coupling to central drive mechanisms, or also via drives provided within the spinning position, which can be laid out as controllable drives if desired.
The spinning position furthermore is equipped, in a manner known as such, in such a manner that the free yarn end is positioned, and as the refining means is re-started, can be taken off in timing coordination. The spinning position is equipped for severing or tearing the longitudinal fibre array before the spinning process is resumed in a manner defined as exactly as possible, which advantageously can be reproduced in exact manner.